1. Field of the Invention
The present invention relates to a process for the determination of controlled variables for the inking unit of printing presses, by means of an ink control and regulation system with ink measurement devices, such as densitometers, for the zone-wise determination of measured values for the printed inks by means of print control strips, which are printed on the printed sheet, whereby the zonally-determined measured values are compared with specified zonal values and zonal variances are determined, taking specified tolerances into account. The individual ink zones are then controlled on the basis of the zonal variances, according to determined algorithms.
With the print control strips used here, single color solid tone (or top tone) measurement fields in each ink zone are primarily used for zonal control and regulation according to the measured values determined. "Solid tone regulation" is advantageous primarily because the only variable involved in the solid tone measurement, or DV, is the saturation as a measurement of the thickness of the ink layer. The classification of the measured value within the printing process is therefore clear. A disadvantage of pure solid tone control is that in spite of the same solid tone density, the printed product and the master, observed visually, do not necessarily agree. There are a number of reasons for this, e.g., different inks, different printing stocks, etc.
Practical tests have determined that when using single color dot halftone fields for ink regulation, in many cases, but not always, a better agreement can be achieved between the master and the printed copy, although variables can also enter into the halftone density value (or DR or screen density) which are independent of the coloration itself. These include the pressure between the plates and rubber blanket cylinder, the printing stock, the rubber blanket, the wetting agent and the wetting agent delivery, the printing plate, as well as slip and doubling.
Values derived from the solid tone density (DV) and the halftone density (DR) can also be used for the ink regulation. By means of the Murray-Davies equation, the tonal value of the printed area (or the tonal value of the printed halftones) can be determined from DV and DR as a controlled variable: F=(1-10.sup.-DR):(1-10.sup.-DV).
Both in regulation according to DR and also in that based on the tonal value of the printed area F, measurement strips are used in which single color dot halftone fields are present for all printing inks in each ink zone. In contrast to the DV regulation, where the solid tone fields dominate in the measurement strips, halftone fields predominate here. All the other fields are present less frequently.
2. Description of the Prior Art
In such ink control and regulation systems (German Laid Open Patent Appln. No. DE-OS 27 28 738), zonal variances are determined on the basis of zonally determined measured values for the printed inks and zonal setpoints, taking into consideration the specified tolerances. From these variances, and on the basis of specified algorithms for the relationship between measurements and ink gap, and on the basis of the ink ductor as a function of the ink gap set and the ink strip set, a new adjustment of the ink gap and/or of the ink strip is determined. The ink measurement devices used for this purpose, such as a scanning densitometer and a multi-channel densitometer, determine the measurement location in addition to the measured values. According to purely geometric functions, the location is assigned to an ink zone, corresponding to the ink zone distribution of the machine in question.
In another embodiment of the prior art (German Utility Model No. DE-GM 77 19 012), a "two-zone" print control strip is used, which is provided only for the measurement and the indication of measurements by ink zone.
Therefore, on all the ink regulation systems used up to now, print control strips are exclusively used which exhibit corresponding solid tone or halftone fields in each ink zone. This has a series of disadvantages with regard to costs, flexibility and the amount of date to be processed.
3. Description of Related Arts
In European Patent Appln. No. RS 74162 CH, an ink control and regulation process is described which is based on chromatometry/colorimetrics, in which multicolor dot halftone fields are used to particular advantage. The measurement apparatus proposed for the execution of this process allow, in addition to the recording of spectra, also their digital filtering, like that performed by ordinary densitometer color filters. Thereby, a selection can be made between control/regulation according to spectral measured values from single or multicolored dot halftone fields or single color solid tone fields, or control/regulation based on densitometric measured values from the same fields. Preferably, a "colorimetric tuning" is conducted, i.e., the printed copy and the master are brought into agreement, and the production run is monitored densitometrically.
Since the various measurement fields for the individual colors in the measurement strip are necessarily located next to one another, the measurement locations are often very different in relation to the ink zone center, for example, and their assignment to a determined ink zone cannot be clearly determined by the process, at least if the measurement point is close to the boundary of the ink zone. Such a measurement value could be unquestionably assigned to either ink zone. If we also take into consideration the lateral compensation by the traversing distributing cylinder of the printing press, which as a rule exhibits a distribution distance which is greater than the width of the ink zone, then the inconclusive nature of the assignment of the measured value and the questionability of the representative nature of the measurement for the zone to which it is assigned becomes clear.
In the so-called "two-zone measurement", in which on the measurement strip, there are solid tone measurement fields for each color in each second ink zone, the zonal color compensation which occurs on account of the lateral distribution is utilized. In general, the lateral distribution distance is the same as the width of one ink zone, plus a slight overrun. Practice has shown that on the basis of a "two-zone measurement", the ink delivery can be controlled manually with sufficient precision.